1. Field of the Invention
The present invention relates to an ink set and an image forming method, and particularly to an ink set and an image forming method preferably using an ink jet recording method for applying at least an ink to a recording medium, and capable of forming a high quality image on plain paper used as the recording medium at a high speed.
2. Description of the Related Art
The ink jet recording method is conventionally used for a printer, a copying machine, and the like because of low noise, low running cost, ease of miniaturization of an apparatus, ease of formation of a color image, etc.
These printing apparatuses using the ink jet recording method have recently been made capable of forming color images of high quality equivalent or substantially equivalent to photographs. However, various ink jet recording techniques have been proposed for the user""s requests to further improve the quality of an ink jet recorded image and increase the speed of ink jet recording.
For example, Japanese Patent Laid-Open No. 58-128862 discloses an ink jet recording method in which the position of an image to be printed is previously determined, and a printing ink and a treatment solution are printed to overlap each other. In this method, the treatment solution is printed before the printing ink is printed, a recording performance improving liquid is superposed on the printing ink previously printed, or the printing ink is superposed on the treatment solution previously printed, and then the treatment solution is further superposed on the printing ink. Similar printing methods are disclosed in Japanese Patent Laid-Open Nos. 63-60783, 64-69381, etc. However, according to the research by the inventors, any one of the above methods cannot be said to be sufficient to further improve the quality of a recorded image, e.g., sufficient to highly satisfy the characteristics such as feathering, bleeding, a coloring property, and a fixing property. Also, these methods cannot be said to cope with variations in image quality and the fixing speed according to the type of the recording medium used.
It is an object of the present invention to provide an ink set and an image forming method capable of highly stably satisfying requirements for the characteristics such as feathering, bleeding, a fixing property and a color tone even when images are formed on various recording media, for example, various types of commercial plain paper.
The object of the present invention is achieved by the following construction. In an aspect of the present invention, an ink set comprises a combination of a recording performance improving liquid for improving the recording performance of ink jet ink, and ink jet ink for forming an image on a recording medium by an ink jet recording method, wherein the recording performance improving liquid contains at least cationic resin fine particles, the ink jet ink contains an organic pigment as a colorant, and the difference between the zeta potentials of the recording performance improving liquid and the ink jet ink is 30 mV or more.
In another aspect of the present invention, an image forming method of forming an image using the above-described ink set comprises (i) the step of applying an ink jet ink constituting the ink set to a recording medium by an ink jet method, and (ii) the step of applying a recording performance improving liquid constituting the ink set to the recording medium, wherein the steps (i) and (ii) are performed so as to bring the ink and the recording performance improving liquid into contact with each other on the recording medium.
As a result of intensive research for solving the problem of the conventional techniques, the inventors found that ink jet recording using an ink set having the above construction permits the satisfactory resolution of the problem of feathering when a color image is formed on a recording medium referred to as xe2x80x9cplain paperxe2x80x9d, the problem of bleeding between different color inks applied on the recording medium, and the problem of difficulties in decreasing the fixing time in recording. This resulted in the achievement of the present invention. It was also found that the image forming method using the ink set of the present invention could obtain a clear recorded image having a good coloring property. In the present invention, the recording performance improving liquid represents a liquid having the function to improve coloring of a colorant, feathering, bleeding, and the fixing property in ink jet recording.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.